Nurses have a prima facie obligation to relieve pain. Nowhere is that obligation more binding than in critically ill patients who are frequently unable to communicate effectively. Yet pain relief is not being achieved as nurses frequently have to balance this obligation against the duty to do no harm. If the dilemma that results from these competing claims is to be resolved, the ethical decision making process of the nurse must be understood. The ethical decision making process can only be adequately understood, however, when it is to pilot test an a priori causal model which explains the decision making process used to assess pain in the critically ill. The latent variables in this nonrecursive model are (1) moral/ethical reasoning, (2) clinical cues, and (3) quality of life judgments. The manifest variable measuring ethical/moral reasoning are modes of reasoning, principles, and mediating factors. The manifest variable which measure clinical cues are physiological and behavioral cues. The manifest variables which measure quality of life judgments are activity, self care, health, social support, and general outlook. The sample consists of 1000 critical care nurses randomly selected from the membership list of the American Association of Critical-Care Nurses. Data collection will consist of a mailed questionnaire packet which contains the Moral Reasoning Instrument, Pain Vignette Instrument, Pain Assessment Survey, Karnofsky Performance Scale, Quality of Life Index, Quality of Life Uniscale and a demographic instrument. Data analysis will include content analysis, descriptive statistics, and structural equation modeling. Pain, a frequent symptom in the critically ill patient, is a dehumanizing experience. In the critical care setting, the patient is often totally dependent on the nurse's assessment for pain management and control. The results of this investigation will provide knowledge which explicates how critical care nurses evaluate and arrive at diagnosis of pain. The ethical/moral and clinical issues surrounding pain can only be addressed when such an explanation is available.